“Some politicians like Tom Cotton voted to cut Social Security. Turn Medicare into a voucher system. And raise the age of eligibility to 70," the ad says. "Not Mark Pryor. Mark’s working to make Social Security and Medicare stronger."

The ad then says Pryor supports cutting billions in waste from entitlement programs, and to provide for lower prescription drug costs and more preventative care.

"I support this message because cutting waste and fraud is responsible, but cutting benefits isn’t,” Pryor says at the end of the ad.

It would raise the eligibility age for Social Security from 65 to 70, and would shift Medicare into a premium support program, which Democrats say would resemble a voucher program. It would also have adopted a less generous formula for raising Social Security benefits for inflation.

The budget was rejected by the House, but won support from the most conservative Republicans.

David Ray, Cotton's campaign spokesman, shot back at Pryor's campaign, arguing the Democrat voted for ObamaCare, which the Congressional Budget Office said would cut $716 billion from Medicare.

“Senator Pryor is already throwing a last minute Hail Mary pass, and the election is still 12 months away. Senator Pryor must be scared to death that his votes for ObamaCare make his re-lection impossible," Ray said in a statement.

"The truth is that Mark Pryor voted to cut $700 billion from today's Medicare recipients while doing nothing to stabilize the program for the future. Senator Pryor has cut Medicare for today's seniors and would let it go broke before tomorrow's seniors even get there. Senator Pryor's lockstep loyalty to President Obama is a bad deal for Arkansas.”

Pryor is seen as one of the most vulnerable Democrats running for reelection to the Senate in 2014.

He voted in favor of the new healthcare law, and Cotton is expected to make that an issue in their campaign. Cotton must first win the Republican nomination for the Senate race.